Complementary air -conditioning system relies on wealth quantity and tube net design without the condition of prepared equipment when the partial equipment fault takes place in air -conditioning system. The system has automatic compensation function that the larger fluctuation will not happen under condition of craftwork assurance. Through this way，the fluctuation problem of process conditions under partial equipment faults in the air -conditioning system is solved. At last，the working principles and design methods of two kinds of complementary air-conditioning systems are introduced.